1. Field of the Invention
Embodiments disclosed herein relate generally to the removal of subsea wellhead assemblies and, more particularly, to the cutting of well casing below a wellhead to enable removal of the wellhead. Specific embodiments relate to cutting the casing and removing the wellhead in a single trip.
2. Description of the Related Art
When an oil or gas well is to be abandoned, government regulations usually require removal of the wellhead. The usual procedure includes steps such as plugging the well with a suitable cement composition, testing the integrity of the plug, and then removing the wellhead assembly. On land, the wellhead assembly can be removed by standard construction techniques and in general, the casing immediately below the wellhead will be cut off several meters below ground level to allow reinstatement of the well site. However, this technique cannot satisfactorily be applied to subsea wells as casings often need to be cut underwater, in situ.
In the case of a subsea well, abandonment usually entails plugging the well bore with cement and then detonating an explosive charge within the well casing slightly below the level of the wellhead in order to cut the casing at that point and free the wellhead assembly for removal. This technique is unsatisfactory because portions of the wellhead removed after explosive cutting can become damaged and not suitable for re-use.
When the use of explosives is not available or desired, other techniques involve severing the casing with a mechanical or hydraulic cutting apparatus. For example, a cutting apparatus is lowered from the surface towards a wellhead, often requiring the assistance of divers or a remotely operated vehicle to affix the apparatus to the wellhead. Once the connection is established, the cutting apparatus is activated to cut the casing. Upon completion of the cutting, the apparatus is disconnected from the wellhead, and raised to the surface. Then, another device or apparatus is subsequently lowered to the wellhead, such that it can affix to the wellhead. Then, the device and wellhead in combination can be raised to the surface. The need for multiple trips is time consuming and inefficient.
Accordingly, there exists a need for an improved cutting module that can perform rigless abandonment operations. There also exists a need for an improved cutting module that can perform a wellhead removal operation in a single trip.